U.S. patent application number 09/814935 was filed with the patent office on 2001-10-11 for speed control apparatus for synchronous reluctance motor.
Invention is credited to Cheong, Dal-Ho.
Application Number | 20010028236 09/814935 |
Document ID | / |
Family ID | 19658603 |
Filed Date | 2001-10-11 |
United States Patent
Application |
20010028236 |
Kind Code |
A1 |
Cheong, Dal-Ho |
October 11, 2001 |
Speed control apparatus for synchronous reluctance motor
Abstract
A speed control apparatus for a synchronous reluctance motor is
disclosed. The speed control apparatus includes a voltage detector
for detecting a voltage applied to the motor, a first phase
converter for receiving voltages in three phases from the voltage
detector and converting the three-phase voltages into equivalent
voltages in two phases, a current detector for detecting a current
applied to the motor, a second phase converter for receiving
currents in three phases from the current detector and converting
the three-phase currents into equivalent currents in two phases,
and a rotor speed operator for receiving the two-phase voltages
thereby computing a speed of a rotor included in the motor. A speed
controller for receiving a deviation between a speed command
externally inputted and an output value from the rotor speed
operator is provided for generating a torque-related current
command. A current controller receives a deviation between a torque
current command externally inputted and an output value from the
rotor speed operator thereby outputting a torque-related current
command. A current controller for receives a deviation between the
torque-related current command and a torque-related current
outputted from the second phase converter, thereby outputting a
torque-related voltage command along with a magnetic-flux-related
voltage command.
Inventors: |
Cheong, Dal-Ho; (Seoul,
KR) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Family ID: |
19658603 |
Appl. No.: |
09/814935 |
Filed: |
March 23, 2001 |
Current U.S.
Class: |
318/701 |
Current CPC
Class: |
H02P 25/08 20130101 |
Class at
Publication: |
318/701 |
International
Class: |
H02P 001/46; H02P
003/18; H02P 005/28; H02P 007/36 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 25, 2000 |
KR |
15348/2000 |
Claims
What is claimed is:
1. A speed control apparatus for a synchronous reluctance motor
comprising: a voltage detector for detecting a voltage applied to
the synchronous reluctance motor; a first phase converter for
receiving voltages in three phases outputted from the voltage
detector based on the voltage detection thereof, and converting the
three-phase voltages into equivalent voltages in two phases; a
current detector for detecting a current applied to the synchronous
reluctance motor; a second phase converter for receiving currents
in three phases outputted from the current detector based on the
current detection thereof, and converting the three-phase currents
into equivalent currents in two phases; and a rotor speed operator
for receiving the two-phase voltages outputted from the first phase
converter, thereby computing a speed of a rotor included in the
synchronous reluctance motor.
2. The speed control apparatus according to claim 1 further
comprising a speed controller for receiving a deviation between a
speed command externally inputted and an output value from the
rotor speed operator, thereby generating a torque-related current
command.
3. The speed control apparatus according to claim 2 further
comprising: a current controller for receiving a deviation between
a torque current command externally inputted and an output value
from the rotor speed operator, thereby outputting a torque-related
current command; a current controller for receiving a deviation
between the torque-related current command outputted from the speed
controller and a torque-related one of the two-phase currents
outputted from the second phase converter, thereby outputting a
torque-related voltage command along with a magnetic-flux-related
voltage command; a voltage generator for converting the two-phase
voltage commands, outputted from the current controller, into
voltages in three phase; and an inverter for conducting a pulse
width modulation for the three-phase voltages outputted from the
voltage generator, and applying the resultant voltages to the
synchronous reluctance motor.
4. The speed control apparatus according to claim 1, further
comprising: a magnetic command generator for receiving the output
value from the rotor speed operator, thereby detecting a positive
torque range and a positive output range in accordance with a
rotating speed of the synchronous reluctance motor, and outputting
a magnetic-flux-related current command; a magnetic flux controller
for receiving a deviation between the output signal from the
magnetic command generator and a magnetic-flux-related one of the
two-phase currents outputted from the second phase converter,
thereby conducting a magnetic flux control for the current
controller to generate the magnetic-flux-related voltage command;
and a magnetic flux angle operator for receiving the output value
from the rotor speed operator, thereby computing a magnetic flux
angle for a coordinate conversion.
5. The speed control apparatus according to claim 3, further
comprising: a magnetic command generator for receiving the output
value from the rotor speed operator, thereby detecting a positive
torque range and a positive output range in accordance with a
rotating speed of the synchronous reluctance motor, and outputting
a magnetic-flux-related current command; a magnetic flux controller
for receiving a deviation between the output signal from the
magnetic command generator and a magnetic-flux-related one of the
two-phase currents outputted from the second phase converter,
thereby conducting a magnetic flux control for the current
controller to generate the magnetic-flux-related voltage command;
and a magnetic flux angle operator for receiving the output value
from the rotor speed operator, thereby computing a magnetic flux
angle for a coordinate conversion.
6. The speed control apparatus according to claim 1, wherein the
rotor speed operator comprises: an induced voltage operator for
receiving respective outputs from the first and second phase
converters, thereby calculating a voltage actually induced in the
motor; an excited current operator for receiving the respective
outputs from the first and second phase converters, thereby
calculating an excited current in the motor; an induced voltage
estimating operator for receiving the outputs from the second phase
converter, thereby estimating a voltage induced in the motor; an
excited current estimating operator for receiving an output from
the induced voltage estimating operator, thereby estimating a
current excited in the motor; a first proportional-integral
controller for receiving a deviation between respective outputs
from the induced voltage operator and the induced voltage
estimating operator, thereby conducting a proportional-integral
control; and a second proportional-integral controller for
receiving a deviation between respective outputs from the excited
current operator and the excited current estimating operator,
thereby conducting a proportional-integral control.
7. The speed control apparatus according to claim 6, wherein said
first proportional-integral controller outputs an estimated speed
value.
8. The speed control apparatus according to claim 7, wherein said
estimated speed value is outputted to the induced voltage
estimating operator.
9. The speed control apparatus according to claim 6, wherein said
second proportional-integral controller outputs a resultant value
from said proportional-integral control to the induced voltage
estimating operator to achieve an inductance compensation depending
on a load applied to said motor.
10. The speed control apparatus according to claim 3, wherein the
rotor speed operator comprises: an induced voltage operator for
receiving respective outputs from the first and second phase
converters, thereby calculating a voltage actually induced in the
motor; an excited current operator for receiving the respective
outputs from the first and second phase converters, thereby
calculating an excited current in the motor; an induced voltage
estimating operator for receiving the outputs from the second phase
converter, thereby estimating a voltage induced in the motor; an
excited current estimating operator for receiving an output from
the induced voltage estimating operator, thereby estimating a
current excited in the motor; a first proportional-integral
controller for receiving a deviation between respective outputs
from the induced voltage operator and the induced voltage
estimating operator, thereby conducting a proportional-integral
control; and a second proportional-integral controller for
receiving a deviation between respective outputs from the excited
current operator and the excited current estimating operator,
thereby conducting a proportional-integral control.
11. The speed control apparatus according to claim 10, wherein said
first proportional-integral controller outputs an estimated speed
value.
12. The speed control apparatus according to claim 11, wherein said
estimated speed value is outputted to the induced voltage
estimating operator.
13. The speed control apparatus according to claim 10, wherein said
second proportional-integral controller outputs a resultant value
from said proportional-integral control to the induced voltage
estimating operator to achieve an inductance compensation depending
on a load applied to said motor.
14. A method of controlling operating speed and operating torque
for a synchronous reluctance motor, said method comprising the
steps of: detecting each phase current and each phase voltage of
said motor; and controlling rotating speed and torque of said motor
based on inductance variations determined from each phase current
and each phase voltage of a stator of said motor.
15. The method according to claim 8 further comprising the steps
of: determining a deviation between a desired speed command and an
estimated speed value of a rotor of said motor; determining a
magnetic flux angle of the rotor based on said estimated speed
value; converting detected voltages and detected currents of said
motor in three phases into converted two phase voltages and
currents, respectively; calculating an induced voltage of said
motor based on said converted two phase voltages and currents,
respectively; generating a current command corresponding to torque
in a q-axis direction of a rotating coordinate system of said motor
based on said deviation; and generating a second current command
corresponding to magnetic flux in a d-axis direction of said
rotating coordinate system.
16. The method according to claim 15, further comprising the step
of determining said estimated speed value based on a deviation
between said induced voltage and an estimated induced voltage.
17. The method according to claim 16, wherein proportional-integral
control is used to determine said estimated speed value.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a speed control apparatus
for a synchronous reluctance motor, and more particularly to a
speed control apparatus for a synchronous reluctance motor which
can accurately control the rotating speed of the motor, in
accordance with a variation in load, without using any sensor
adapted to detect the position of a rotor included in the motor.
Description of the Related Art
[0003] A synchronous motor, which is a kind of an AC motor, is a
constant-speed motor which rotates at a fixed speed, irrespective
of the load applied thereto at a certain frequency, that is, at a
synchronous speed. In particular, in a synchronous reluctance
motor, torque is generated, based on reluctance components.
Accordingly, the rotation of the rotor included in the synchronous
reluctance motor results from only a reluctance torque.
[0004] FIG. 1 is a plan view schematically illustrating a
configuration of a conventional three-phase synchronous reluctance
motor.
[0005] Referring to FIG. 1, the conventional three-phase
synchronous reluctance motor, which is denoted by the reference
numeral 100, includes a stator 101 adapted to create a rotating
magnetic field upon receiving an AC voltage applied thereof, and a
rotor 102 arranged inside the stator 101 and adapted to rotate by
virtue of the rotating magnetic field created by the stator
101.
[0006] As shown in FIG. 2, the rotor 102 is divided into four
regions each formed with grooves 102h. The grooves 102h of each
rotor region are symmetrical with those of a facing one of the
remaining rotor regions. The grooves 10h are adapted to generate an
increased difference between a reluctance generated in a d-axis
direction and a reluctance generated in a q-axis direction, thereby
generating a reluctance torque for rotating the rotor 102. In FIG.
2, the reference numeral 102f denotes a flow of magnetic flux
generated by virtue of the magnetic field created by the stator
101.
[0007] FIG. 3 is a block diagram schematically illustrating a
conventional speed control apparatus applied to a three-phase
synchronous reluctance motor having the above-mentioned
configuration.
[0008] As seen in FIG. 3, the conventional speed control apparatus
includes a speed controller 301 for receiving a deviation between a
speed command value outputted from a main control unit (not shown)
and an actual speed of the three-phase synchronous reluctance motor
310 detected by a rotor position detector 309. The speed controller
301 controls the speed of a rotor 102 included in a synchronous
reluctance motor 310 based on the speed deviation. The speed
control apparatus also includes a magnetic flux command generator
305 for receiving an output signal from the rotor position detector
309 and computing a magnetic flux angle of the rotor 102 based on
the received output signal.
[0009] The speed control apparatus also includes a magnetic flux
angle operator 307 for receiving an output signal from the rotor
position detector 309, thereby computing a magnetic flux angle of
the rotor; a coordinate converter 308 for conducting a coordinate
conversion of a three-phase current inputted to the synchronous
reluctance motor 310 into a two-phase; and a magnetic flux
controller 306 for receiving an output signal from the magnetic
flux command generator 305 and an output from the coordinate
converter 308, thereby controlling a magnetic flux-related
current.
[0010] The speed control apparatus further includes a current
controller 302 for receiving a deviation between an output signal
from the speed controller 301 and the output signal from the
coordinate converter 308, along with an output signal from the
magnetic flux controller 306, thereby generating a torque-related
voltage command and a magnetic flux-related command. The speed
control apparatus also includes a voltage generator 303 for
receiving the torque-related voltage command and magnetic
flux-related command outputted from the current controller 302 and
the output signal from the magnetic flux angle operator 307,
thereby outputting a three-phase voltage command. An inverter 304
receives the three-phase voltage command from the voltage generator
303 and supplies an AC voltage corresponding to the received
three-phase voltage command to the three-phase synchronous
reluctance motor 310.
[0011] In the conventional speed control apparatus having the
above-mentioned configuration, the speed controller 301 receives a
deviation between a speed command outputted from the main control
unit (not shown) and a speed value of the three-phase synchronous
reluctance motor 310 fed back from the rotor position detector 309.
The speed controller 301 then outputs a current command
i.sub.qs.sup.* relating to a torque in the q-axis direction of a
rotating coordinate system, based on the received speed
deviation.
[0012] The magnetic flux command generator 305 detects a positive
torque range and a positive output range from the output signal
from the rotor position detector 309, thereby outputting a current
command i.sub.ds.sup.* relating to magnetic flux in the d-axis
direction of the rotating coordinate system. The magnetic flux
controller 306 receives a deviation between the
magnetic-flux-related current value i.sub.ds.sup.* outputted from
the magnetic flux command generator 305, and a two-phase-converted
magnetic-flux-related current value i.sub.ds outputted from the
coordinate converter 308, thereby controlling a
magnetic-flux-related current.
[0013] The magnetic flux angle operator 307 receives the output
signal from the rotor position detector 309, thereby computing a A
magnetic flux angle {circumflex over (.theta.)} of the rotor. Based
on the magnetic flux angle {circumflex over (.theta.)}, the
coordinate converter 308 conducts a coordinate conversion for a
three-phase current inputted to the synchronous reluctance motor
310 into a two-phase, that is, a q and d-axis phase.
[0014] The current controller 302 receives the torque-related
current command i.sub.qs.sup.* and the magnetic-flux-related
current command i.sub.ds.sup.*, and generates a torque-related
voltage command V.sub.qs.sup.* and a magnetic-flux-related voltage
command V.sub.ds.sup.*, respectively. The torque-related voltage
V.sub.qs.sup.* and magnetic-flux-related voltage commands
V.sub.ds.sup.* are applied to the voltage generator 303, which also
receives the magnetic flux angle {circumflex over (.theta.)} from
the magnetic flux angle operator 307. Based on these received
signals, the voltage generator 303 outputs three-phase voltage
commands V.sub.as, V.sub.bs, and V.sub.cs. The inverter 304 then
applies a corresponding voltage to the synchronous reluctance motor
310 based on the three-phase voltage commands V.sub.as, V.sub.bs,
and V.sub.cs.
[0015] In a speed control apparatus according to the
above-mentioned conventional synchronous reluctance motor, a sensor
such as an encoder or a hall IC is used for the rotor position
detector 309 and adapted to obtain information about the position
of the rotor. However, there are various technical difficulties
with an application of such a sensor to refrigerators or air
conditioners.
SUMMARY OF THE INVENTION
[0016] The present invention has been made in view of the above
mentioned problems, and an object of the invention is to provide a
speed control apparatus for a synchronous reluctance motor which
can accurately control the rotating speed of the motor by detecting
only the current and voltage of each phase flowing in the motor
without using any separate sensor that is necessarily adapted to
detect the position of a rotor included in the motor.
[0017] These and other objects are accomplished by a speed control
apparatus for a synchronous reluctance motor comprising a voltage
detector for detecting a voltage applied to the synchronous
reluctance motor; a first phase converter for receiving voltages in
three phases outputted from the voltage detector based on the
voltage detection thereof, and converting the three-phase voltages
into equivalent voltages in two phases; a current detector for
detecting a current applied to the synchronous reluctance motor; a
second phase converter for receiving currents in three phases
outputted from the current detector based on the current detection
thereof, and converting the three-phase currents into equivalent
currents in two phases; and a rotor speed operator for receiving
the two-phase voltages outputted from the first phase converter,
thereby computing a speed of a rotor included in the synchronous
reluctance motor.
[0018] These and other objects are further accomplished by a method
of controlling operating speed and operating torque for a
synchronous reluctance motor, the method comprising the steps of
detecting each phase current and each phase voltage of said motor;
and controlling rotating speed and torque of said motor based on
inductance variations determined from each phase current and each
phase voltage of a stator of said motor.
[0019] In accordance with the present invention, it is possible to
accurately control the rotating speed and torque of the motor by
detecting only the current and voltage applied to the motor without
using any separate sensor adapted to detect the position of a rotor
included in the motor. In order to achieve an enhancement in
control accuracy, an inductance calculation is conducted, and an
inductance compensation is carried out based on the result of the
inductance calculation.
[0020] Advantages of the present invention will become more
apparent from the detailed description given hereinafter. However,
it should be understood that the detailed description and specific
examples, while indicating preferred embodiments of the present
invention, are given by way of illustration only, since various
changes and modifications within the spirit and scope of the
present invention will become apparent to those skilled in the art
from this detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] The present invention will become more fully understood from
the detailed description given hereinbelow and the accompanying
drawings which are given by way of illustration only, and thus do
not limit the present invention.
[0022] FIG. 1 is a plan view schematically illustrating a
configuration of a conventional three-phase synchronous reluctance
motor;
[0023] FIG. 2 is a view illustrating the operation of a rotor
included in the synchronous reluctance motor shown in FIG. 1;
[0024] FIG. 3 is a block diagram schematically illustrating a
conventional speed control apparatus applied to a three-phase
synchronous reluctance motor having the configuration of FIG.
1;
[0025] FIG. 4 is a block diagram illustrating a speed control
apparatus for a synchronous reluctance motor according to the
present invention;
[0026] FIG. 5 is a block diagram illustrating a rotor speed
operator included in the speed control apparatus of FIG. 4;
[0027] FIG. 6 is a graph depicting a variation in the inductance of
a general synchronous reluctance motor;
[0028] FIG. 7 is a graph depicting respective vector variations of
the voltage and current in a general synchronous reluctance motor;
and
[0029] FIG. 8 is a graph depicting a variation in the inductance of
a general synchronous reluctance motor depending on a variation in
current.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0030] Referring to FIG. 4, a speed control apparatus for a
synchronous reluctance motor according to the present invention is
illustrated. As shown in FIG. 4, the speed control apparatus
includes a voltage detector 412 for detecting a voltage applied to
the synchronous reluctance motor denoted by the reference numeral
413, a first phase converter 411 for receiving voltages V.sub.as,
V.sub.bs, and V.sub.cs in three phases outputted from the voltage
detector 412 based on the voltage detection thereof, and converting
those three-phase voltages V.sub.as, V.sub.bs, and V.sub.cs into
equivalent voltages V.sub.ds and V.sub.qs in two phases.
[0031] A current detector 409 for detecting a current applied to
the synchronous reluctance motor 413 is provided with a second
phase converter 408 for receiving currents i.sub.as, i.sub.bs, and
i.sub.cs in three phases outputted from the current detector 409,
and converting those three-phase currents i.sub.as, i.sub.bs, and
i.sub.cs into equivalent currents i.sub.ds and i.sub.qs in two
phases.
[0032] The speed control apparatus also includes a rotor speed
operator 410 for receiving the two-phase voltages V.sub.ds and
Vq.sub.qs outputted from the first phase converter 411, thereby
computing the speed of a rotor included in the synchronous
reluctance motor 413. A speed controller 401 for receiving a
deviation between a speed command .omega..sub.r.sup.* externally
inputted and an output value {circumflex over (.omega.)}.sub.r from
the rotor speed operator 410 is provided for generating a current
command i.sub.qs.sup.* relating to torque in the q-axis direction
of a rotating coordinate system.
[0033] A magnetic flux command generator 405 for receiving the
output signal from the rotor speed operator 410 is provided for
detecting a positive torque range and a positive output range in
accordance with the rotating speed of the synchronous reluctance
motor 413, and outputting a current command i.sub.ds.sup.* relating
to magnetic flux in the d-axis direction of the rotating coordinate
system. A magnetic flux controller 406 for receiving a deviation
between the output signal i.sub.ds.sup.* from the magnetic command
generator 405 and the current i.sub.ds from the second phase
converter 408 relating to magnetic flux in the d-axis direction of
the rotating coordinate system is provided for controlling magnetic
flux.
[0034] The speed control apparatus further includes a magnetic flux
angle operator 407 for receiving the output signal from the rotor
speed operator 410, thereby computing a magnetic flux angle
{circumflex over (.theta.)} for a coordinate conversion. A current
controller 402 for receiving a deviation between the torque current
command i.sub.qs.sup.* from the speed controller 401 and the
current i.sub.qs from the second phase converter 408 relating to
torque in the q-axis direction of the rotating coordinate system,
along with an output signal from the magnetic flux controller 406,
outputs a torque-related voltage command V.sub.qs.sup.* and a
magnetic-flux-related voltage command V.sub.ds.sup.* to the voltage
generator 403.
[0035] The voltage generator 403 converts the two-phase voltage
commands V.sub.qs.sup.* and V.sub.ds.sup.* into voltages V.sub.as,
V.sub.bs, and V.sub.cs in three phases, and then outputs the
three-phase voltages V.sub.as, V.sub.bs, and V.sub.cs. An inverter
404 receives the three-phase voltages V.sub.as, V.sub.bs, and
V.sub.cs from the voltage generator 403, conducts a pulse width
modulation for those three-phase voltages V.sub.as, V.sub.bs, and
V.sub.cs, and applies the resultant modulated voltages to the
synchronous reluctance motor 413.
[0036] As shown in FIG. 5, the rotor speed operator 410 includes an
induced voltage operator 501 for receiving respective outputs from
the first and second phase converters 411 and 408, and calculating
the voltage actually induced in the motor 413. An excited current
operator 502 for receiving respective outputs from the first and
second phase converters 411 and 408 is provided which calculates an
excited current in the motor 413.
[0037] An induced voltage estimating operator 503 for receiving the
output from the second phase converter 408, estimates a voltage
induced in the motor 413. An excited current estimating operator
504 receives an output from the induced voltage estimating operator
503, thereby estimating a current excited in the motor 413.
[0038] The rotor speed operator 410 includes a first
proportional-integral controller 505 for receiving a deviation
between respective outputs from the induced voltage operator 501
and induced voltage estimating operator 503, thereby conducting a
proportional-integral control. The rotor speed operator 410 also
includes a second proportional-integral controller 506 for
receiving a deviation between respective outputs from the excited
current operator 502 and excited current estimating operator 504,
thereby conducting a proportional-integral control.
[0039] The operation of the speed control apparatus of the present
invention having the above-mentioned configuration will now be
described in conjunction with FIGS. 4 to 8.
[0040] The speed controller 401 receives a deviation between a
speed command .omega..sub.r.sup.* inputted from the main control
unit (not shown) to the system and a speed value {circumflex over
(.omega.)}.sub.r estimated for a speed of the synchronous
reluctance motor 413 and fed back from the rotor speed operator
410. The speed controller 401 then generates a current command
i.sub.qs.sup.* relating to torque in the q-axis direction of the
rotating coordinate system based on these received values.
[0041] The magnetic flux command generator 405 receives the
estimated speed value {circumflex over (.omega.)}.sub.r, detects a
positive torque range and a positive output range, and outputs a
current command i.sub.ds.sup.* relating to magnetic flux in the
d-axis direction of the rotating coordinate system. The magnetic
flux controller 406 receives a deviation between the
magnetic-flux-related current command i.sub.ds.sup.* from the
magnetic flux command generator 405 and a current i.sub.ds from the
second phase converter 408 relating to magnetic flux in the d-axis
of the rotating coordinate system. The magnetic flux controller 406
controls magnetic flux in response to the received deviation.
[0042] The estimated speed value {circumflex over (.omega.)}.sub.r
outputted from the rotor speed operator 410 is also applied to the
magnetic flux angle operator 407. The magnetic flux operator 407,
in turn, computes a magnetic flux angle {circumflex over (.theta.)}
of the rotor based on the received value. The first and second
phase converters 411 and 408, respectively, convert voltages in
three phases and currents in three phases detected from the
synchronous reluctance motor 413 and based on the magnetic flux
angle {circumflex over (.theta.)}, into two phases corresponding to
the q and d-axes of the rotating coordinate system,
respectively.
[0043] The induced voltage operator 501 included in the rotor speed
operator 410 receives the two-phase voltages V.sub.ds and V.sub.qs
and the two-phase currents i.sub.ds and i.sub.qs respectively
outputted from the first and second phase converters 411 and 408.
The induced voltage operator calculates a voltage actually induced
in the synchronous reluctance motor 413 based on the voltages and
currents it receives. This induced voltage em is derived using the
following Equation 1:
[0044] [Equation 1]
e.sub.m=V.sub.s-r.sub.s.multidot.i.sub.s
[0045] where, "e.sub.m", "V.sub.s", and "i.sub.s" represent the
induced voltage, the input voltage to the motor 413, and the input
current to the motor 413, respectively.
[0046] In order to achieve an estimation for a speed of the motor
413, a deviation between the output e.sub.m from the induced
voltage operator 501 and an output .sub.m from the induced voltage
estimation operator 503, "e.sub.m-.sub.m", is inputted to the first
proportional-integral controller 505. The first
proportional-integral controller 505 conducts a
proportional-integral control based on the received deviation
"e.sub.m-.sub.m", thereby outputting an estimated speed {circumflex
over (.omega.)}.sub.r, of the motor 413. The speed controller 401
then receives a deviation between the speed command
.omega..sub.r.sup.* and the estimated speed {circumflex over
(.omega.)}.sub.r, thereby outputting a current command
i.sub.qs.sup.* relating to torque in the q-axis direction of the
rotating coordinate system.
[0047] Concurrently, and as shown in FIG. 8, respective inductances
L.sub.d and L.sub.q resulting from a load concurrently applied to
the motor 413 exhibit different variations from each other in
accordance with the input current. Since there is a great
difference in inductance between a low load and a high load, it is
necessary to compensate for an inductance resulting from a load
applied to the motor 413.
[0048] Therefore, a deviation between an output i.sub.m from the
excited current operator 502 and an output .sub.m from the excited
current estimating operator 504, that is, "i.sub.m-.sub.m", is
applied to the second proportional-integral controller 506. The
second proportional-integral controller 506, in turn, conducts a
proportional-integral operation for the input value, and outputs
the resultant value to the inducted voltage estimating operator 503
so as to achieve an inductance compensation depending on the load
applied to the motor 413.
[0049] The current controller 402 receives a deviation between the
torque-related current command i.sub.qs.sup.* and the
torque-related current i.sub.qs outputted from the second phase
converter 408, along with the output signal from the magnetic flux
controller 406, thereby outputting a torque-related voltage command
V.sub.qs.sup.* and a magnetic-flux-related voltage command
V.sub.ds.sup.*. These torque-related voltage V.sub.qs.sup.* and
magnetic-flux-related voltage commands V.sub.ds.sup.* are applied
to the voltage generator 403, which also receives the magnetic flux
angle {circumflex over (.theta.)} from the magnetic flux operator
407.
[0050] The voltage generator 403 then generates voltages V.sub.as,
V.sub.bs, and V.sub.cs in three phases based on the received
values. The three-phase voltages V.sub.as, V.sub.bs, and V.sub.cs
are then applied to the inverter 404, which in turn conducts a
pulse width modulation for the applied voltages and applies the
resultant voltages to the synchronous reluctance motor 413.
[0051] As shown in FIG. 6, the synchronous reluctance motor 413
exhibits an inductance variation characteristic during a rotation
of the rotor conducted in accordance with the three-phase voltages
applied to the motor 413. Referring to FIG. 6, it can be found that
the inductance variation depends on the rotating angle of the
rotor. Accordingly, when the inductance variation is derived by
detecting the input voltage and current of the stator included in
the motor 413, it is possible to determine the position of the
rotor. Thus, the speed of the rotor can be controlled using the
derived inductance variation.
[0052] FIG. 7 is a graph depicting the vectors showing the
relationships among the position of the rotor, the voltage applied
to the motor, and the current applied to the motor.
[0053] Referring to the vector diagram of FIG. 7, the voltage
applied to the synchronous reluctance motor can be expressed by the
following Equations 2 and 3:
[0054] [Equation 2]
V.sub.ds=r.sub.si.sub.ds+d(.lambda..sub.ds)/dt-.omega..sub.r.lambda..sub.q-
s
[0055] [Equation 3]
V.sub.qs=r.sub.si.sub.qs+d(.lambda..sub.qs)/dt+.omega..sub.r.lambda..sub.d-
s
[0056] where, "V.sub.ds" and "V.sub.qs" represent respective stator
voltages in the d and q-axis directions, "r.sub.s" represents the
resistance of the stator, "i.sub.ds" and "i.sub.qs" represent
respective stator currents in the d and q-axis directions,
".lambda..sub.ds" and ".lambda..sub.qs" respective magnetic fluxes
in the d and q-axis directions, and ".omega..sub.r" represents the
rotor speed of the motor.
[0057] Since .lambda..sub.ds=L.sub.di.sub.s, and
.lambda..sub.qs=L.sub.qi.- sub.s, it is possible to calculate the d
and q-axis inductances L.sub.d and L.sub.q by detecting the
associated voltages and currents. Since the calculated d and q-axis
inductances vary in accordance with a shifted position of the rotor
included in the rotor of FIG. 2, it is possible to find information
about the position of the rotor by calculating, in real time, those
inductances.
[0058] Based on the inductance variations, an estimated value
{circumflex over (.omega.)}.sub.r for the rotor speed .omega..sub.r
can be calculated. Accordingly, it is possible to control the speed
of the motor by comparing the A estimated speed {circumflex over
(.omega.)}.sub.r with the speed command .omega..sub.r.sup.*.
[0059] As is apparent from the above description, the present
invention provides a speed control apparatus for a synchronous
reluctance motor which can accurately control the rotating speed
and torque of the motor by detecting only the current and voltage
of each phase flowing in the motor without using any separate
sensor, such as an encoder or a hall IC necessarily adapted to
detect the position of a rotor included in the motor.
[0060] Further, an inductance calculation is conducted and an
inductance compensation is carried out based on the result of the
inductance calculation in order to achieve an enhancement in
control accuracy. Thus, it is possible to achieve an effective
control system for the rotating speed of the motor with increased
accuracy. In addition, for an application involving a difficult
detection for the position and speed of a rotor, such as in the
compressor of a refrigerator or air conditioner, the present
invention is ideally suited as a means of accurately detecting
rotor position and controlling rotor speed with a simplified
system.
[0061] The present invention being thus described, it will be
obvious that the same may be varied in many ways. Such variations
are not to be regarded as a departure from the spirit and scope of
the present invention, and all such modifications as would be
obvious to one skilled in the art are intended to be included
within the scope of the following claims.
* * * * *